An analog to digital converter (ADC) converts an analog signal into a discrete binary code suitable for digital processing. There are several factors that determine whether or not a particular ADC is suited to a particular application, including complexity, cost, conversion time, resolution, accuracy and performance over temperature. However, the ADC's currently available have numerous deficiencies in one or more of those areas.
U.S. Pat. No. 3,968,486 teaches an ADC that utilizes a plurality of analog comparators, wherein each comparator receiving an analog input signal and a separate unique reference signal. The total analog to digital conversion time is nT, where n is the number of comparator stages and T is the response time of the comparator. U.S. Pat. No. 4,599,602 teaches a serial-type ADC utilizing folding circuit cells. The first cell receives a reference voltage. Each cell's output signal polarities are inverted with respect to the input signal polarities. The output of this ADC is direct-gray binary reflected code, not a natural binary code. Additional circuitry is required to convert the output to natural binary.
It is one object of the invention to provide an ADC that has a very low parts count, thereby reducing complexity and cost while increasing accuracy.
It is another object of the invention to provide an ADC in which all ADC cells employ a common reference signal.
It is another object of the invention to provide an ADC in which the conversion rate remains constant as a resolution of an output binary code increases.
It is another object of the invention to provide an ADC that includes an analog delay-line function.
It is another object of the invention to provide an ADC having temperature stability.
It is another object of the invention to provide an ADC that can also be used as a digital to analog converter (DAC) without adding components or changing component values.
It is a further object of the invention to provide an ADC that operates to yield true logarithmic compression.
It is one further object of the invention to provide an ADC that has a direct floating point output consistent with industry standard format.
It is also an object of the invention to provide an ADC that uses a single cell in a recursive (cyclic) fashion to provide n-bits of resolution.